The owner of a boat that exploded in Ocean Pines on Sunday afternoon followed procedure by allowing the "blowers" on the inboard-outboard unit to run as long as 15 minutes before he started it, an official said.

The blowers bring outside air into the engine compartment on sterndrive boats like the 24-footer owned by Neil Edwards, a Springfield, Virginia, man who also has a residence on Boatswain Drive, Ocean Pines, where the explosion occurred.

The outside air displaces fuel vapors in the engine compartment, reducing the risk of explosion.

Candy Thomson, a spokeswoman with the Maryland Natural Resources Police, said nothing was amiss when Edwards, who had also opened ventilation hatches, reversed the vessel away from a private dock with four others aboard.

"When he put it in forward gear, it blew up," Thomson said. "He had the blowers on about 10 or 15 minutes."

She did not immediately know the make of the boat or the size of the engine. Neighbors helped get the victims out of the water.

Two passengers who were sitting near the stern and motor suffered burns to their arms and lower legs.

Thompson identified them as Larry MacPherson, 57, Dawn Van Deursena, 49, both of Escondido, California. They were transported to Baltimore's Johns Hopkins Bayview Burn Center in an air ambulance.

Their condition was not immediately known.

"They were expected to be, based on an assessment at the scene, in the hospital for a day or two," Thomson said.

The Worcester County Fire Marshal's Office is assisting in the investigation. An office representative did not have additional information when contacted Monday.

An official at the Ocean Pines Police Department said the investigation was being handled by the Natural Resources Police and fire marshal.

The Ocean Pines Volunteer Fire Department responded and extinguished the blaze. A staffer at the department who was contacted Monday was not on duty when the explosion happened and had no information.